"Active Flow Control for High-Lift of Transport Aircraft"

Speaker: Rolf Radespiel, Technische Universität Braunschweig, Germany

The motivation to use active flow control is rooted in the assumption that active means can improve aerodynamic performance beyond the limits of an optimised geometric shape. In modern aircraft these limits are usually associated with flow separation, resulting in unwanted pressure drag and lift losses. But active means of flow control require additional systems and additional power on board and this appears as a strong barrier against design decisions to use active flow control in commercial aircraft. The lecture will present progress towards overcoming this barrier. While a large range of physical approaches exist to manipulate separating flows it appears that active flow control by well-designed means of blowing is presently the only path suitable for commercial aircraft with large weight and Reynolds numbers. With active blowing there are three general paths for affecting flow separations. The first and most obvious is to increase flow momentum directly by inserting a high-velocity tangential airstream close to the surface. The second is to augment turbulent momentum transport normal to the surface, by exploiting physically relevant means to affect shear flow turbulence and unsteady flow modes. The third path is to redistribute the momentum distribution of the boundary layer by special means of convective transport. The lecture will compare design sensitivities and application ranges for different blowing approaches in this respect, taking into account the efficiency requirements of aircraft. Special attention will be given to dynamic means of flow control. Here the experience from recent flow experiments in water tunnels and wind tunnels will be reported. The results allow for assessing the potentials and limits of dynamic blowing in high-lift of future commercial aircraft.